I would suggest not thinking about it in terms of what it used to be. The site had to evolve. Partly, they needed to stop hemorrhaging money. And partly, the Q&A format has a self-limiting lifespan, where the "fun" questions have long since been asked and answered.
These factors come together in the Quora Partnership Program, where they paid people to add questions in the hope of driving engagement. That results in a flood of uninteresting questions. Even if it worked to bring revenue, it's a qualitatively different kind of site, and the sheer quantity drives away the people who wanted to write good content.
At this point even ending that program may not help, since it both reflects and drives a fundamental change to the site that can't be walked back. They need a new way to engage people. The flood of new modes of interaction seems to confuse people; the site managers are throwing things at the wall to see what sticks.
If it were me I'd try to play to the site's old strengths by fostering a sense of community. In that it overlaps sites like Reddit and even HN, but they can leverage their reputation and existing audience. Promote the comments features, help people locate friendly voices, tamp down hostility before it spreads, and generally encourage people to stay on the site in order to spend time with each other.
They've got a so-so recommendation engine that could be improved. The search feature has been useless for years, and while I'm not sure if fixing it would help save the site, the neglect makes the site feel like a vandalized building with broken windows and graffiti.
